Planktonic Growth of Pseudomonas aeruginosa around a Dual-Species Biofilm Supports the Growth of Fusobacterium nucleatum within That Biofilm

PURPOSE: The goal of this study was to understand the potential interaction between Pseudomonas aeruginosa and Fusobacterium nucleatum within the middle ear. METHODS: We examined the microbiota of ear fluid and tympanostomy tubes (TTs) obtained from patients with posttympanostomy tube otorrhea. We also examined biofilms formed by P. aeruginosa and F. nucleatum, singly or together, under aerobic or anaerobic conditions. RESULTS: While the facultative anaerobe P. aeruginosa dominated the bacterial population within the ear fluid, strict anaerobes, including F. nucleatum, dominated bacterial populations within the TTs. F. nucleatum was able to grow under aerobic conditions only in the presence of P. aeruginosa, whose growth reduced the level of dissolved oxygen within the broth to nearly anoxic condition within 4 h after inoculation. The presence of P. aeruginosa allowed F. nucleatum to maintain its growth for 72 h within the dual-species biofilm but not within the planktonic growth. Visualization of the biofilms revealed coaggregation of P. aeruginosa and F. nucleatum. CONCLUSION: Extrapolation of these results suggests that, within the middle ear fluid, the growth of P. aeruginosa produces the anaerobic conditions required for the growth of F. nucleatum, both within effusion and within biofilms.